This invention generally relates to engine speed control. More particularly, this invention relates to a strategy for controlling engine braking during a gear shift in a vehicle driveline.
A variety of vehicle drivelines are known. In many instances, especially with large trucks, the vehicle transmission includes a large number of available gear ratios. The task of shifting the transmission between the various gear ratios can prove to be complex and challenging, especially for inexperienced drivers. Those skilled in the art are continuously striving to make the task of driving such vehicles easier for drivers.
While various advances have been made, such as providing automated shift actuators and eliminating the requirements for manual clutch control, there is still room for improvement. For example, in systems where a driver is not required to manually operate a clutch, an engine controller controls engine speed to achieve synchronization with a required rotation speed in the gear box to be able to engage a subsequent gear. One attempt at facilitating engine speed control is to apply engine braking during an upshift. In most circumstances, engine braking is applied using rudimentary criteria.
There are several shortcomings in conventional engine braking arrangements. First, most do not accommodate the variations between different vehicles and different driveline components so that the control strategy is not readily adaptable or applicable for more than one vehicle. Another shortcoming is that most control strategies fail to recognize the limitations on the vehicle driveline components, including the engine braking components.
There is a need for an improved engine braking strategy to facilitate more accurate and more reliable synchronization between engine output speed and transmission input speed during assisted shifting procedures. This invention addresses that need while overcoming the shortcomings and drawbacks of prior attempts.
In general terms, this invention is a method of controlling engine speed during a gear shift procedure in a vehicle driveline. The method includes activating an engine brake, which is intended to reduce the engine speed. An expected time when the engine speed will be the same as a desired engine speed is determined. The engine brake is deactivated at a deactivation time before the expected time when the engine speed will be the same as the desired speed. The deactivation time accounts for any delay between the time a request is made to turn off the engine brake and the actual time that the engine brake will shut off in response to that request.
Another aspect of this invention is controlling engine speed during a gear shift procedure by comparing a predicted engine speed value and a predicted speed request. The predicted engine speed value is based upon a sum of a current engine speed value plus the product of an engine acceleration value times an engine brake deactivation time. The predicted speed request is based upon a sum of a requested speed value plus the product of a requested speed acceleration value times the engine brake deactivation time. In one example, whenever the predicted engine speed value is less than the predicted speed request, the engine brake is turned off. Otherwise, the engine brake is turned on, assuming that a gear shift procedure when engine braking is desired is occurring.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.